In the field of bone surgery, particularly in dental techniques, there is often the need to act on the jawbones and on the lower jawbones, with invasive and traumatic operations.
One of the best-known, non-strictly-surgical operations, which nevertheless generates stress for the dental arch and the underlying bone structure, is the removal of a tooth crown. As a matter of fact, a significant effort is required to detach the artificial crown from the tooth stump or from the implant pin anchored in the bone, breaking the bond of general glues or cements without damaging the stump or implant pin from the bone. More invasive actions are the ones relating to implant techniques—for example the insertion of implant pins into the lower jaw bone—which represent surgical procedures by now carried out routinely in dental surgeries. With reference to this last operation mode, in particular, over the last few years insertion procedures of the implant pin into the tooth socket are used, also in the proper body locations with insufficient bone volume and thickness. In order to be able to carry out these implantology procedures in a post-extraction tooth socket (see FIG. 1), however, it is necessary to act on the bone, to create the housing for the implant and possibly to perform an augmentation of the maxillary sinus, in a distal region of the jawbone (see FIGS. 2-4): the horizontal and vertical expansion of the jawbone is traditionally performed by using osteotomes in association with a manual surgical hammer. In particular, the operation may be of three different types:
a. horizontal expansion of the bone ridge of the upper jawbone,
b. vertical expansion of the jawbone, with deformation and shifting of the jawbone floor and sinus,
c. horizontal and vertical expansion of the jawbone (with creation of a vertical slot, in the mesio-distal direction within the mouth-palate thickness of the residual bone ridge, and two releasing intra-bone incisions, a mesial one and a distal one).
However, also in the orthopedic field surgical techniques exist which require the application of percussive actions. For example, the extraction of temporary screws or nails from bone masses requires a hammer percussion action; such operations are often made difficult by the calcification of the screws or of the nails in the bone.
Moreover, for the insertion of prosthesis or connection means into bones, the technique of obtaining also the implant seats, instead of through the use of rotary mills causing wear of bone mass and in biologically unsuitable in-situ overheating, through osteotomes beaten by the manual surgical hammer has become established. Through such technique, sliding and bone compacting is obtained, beat upon beat, which enables the physician to assess each time the result obtained.
In all these cases of bone surgery, the forces/accelerations which can be imparted manually, through a surgical hammer, have a modulus and direction which cannot be pre-determined precisely, neither can they be constant, nor repeatable. The operator hence performs continuous adjustments which make the operation longer and more painful than necessary. Moreover, the forces applied manually last relatively long (in the order of tenths of a second) so that, given their physical nature, they deform the spongy part of the bone in an extremely limited manner; this occurs since the majority of the force is expressed accelerating the entire affected bone structure, for example the cranial-facial one. Consequently, in addition to not producing an effective action localised on the bone, the inertial impacts which reflect on the entire bone structure of the skull may determine influences on the internal part of the patient's ear and painful conditions; as a matter of fact, the patient's head undergoes a significant acceleration, while the otoliths tend to maintain their state due to inertia: an acceleration of the otoliths with respect to the maculae results; in the cases in which the acceleration exceeds the force of adhesion to the cilia, a detachment of the otoliths occurs, due to the large mass thereof compared to the initial speed of the system. This causes vertigo to the patient (Benign Paroxysmal Positional Vertigo, or cupulolithiasis) the main symptom of which is balance distortion, caused by the detachment of the otoliths.
These practices have shown that it is very difficult for the surgeon to be able to maintain the alignments and obtain the correct compacting thickness of the spongy mass of the bone.
Another critical aspect of the manual practice is the execution of the “split crest” technique: the manually caused impact hardly aids the dilation of the bone ridge and easily causes complications, among which the break of the bone ridge, with resulting problems in the positioning of the implant pin.
This comes in addition to the problem concerning the accessibility to the innermost part of the jawbone and of the upper jaw, seat of the molar teeth.
The prior art already offers some electrical devices suited to create more repeatable mechanical actions, which replace the forces which can be manually exercised by the surgeon.
Typically, instruments provided with a longitudinally movable cursor (or mass) through the action of linear motors or of suited configurations with magnetic coil have already been offered.
However, so far these instruments have not proved fully satisfactory for various reasons. They are generally conceived to perform an alternate, vibrational motion of a work tool, which hence substantially allows to perform a cutting/sawing action and in any case with an erosive function with resulting bone mass wear, with minimal forces and with alternate, continuous movement. Since these instruments are not designed to absorb and develop large amounts of energy, they fully differ from the need referred to in the present treatment. The continuity of the alternate action prevents from delivering large amounts of energy. Therefore the short continuous and alternate movements of these devices, even though they do not create the bad clinical conditions listed above, are unable to act as desired on the local bone structure or to effectively detach calcified bridges, crowns or screws.
GB 316,478, for example, describes a tool-actuating device, which includes a moving slider acting like a hammer. The tool is integral with the terminal part of a housing body. The slider is maintained in a home position by a compression spring and is guided in a tubular element: it is accelerated directly against the tool through a solenoid reel. A vulcanised rubber element is furthermore provided between the slider and the tool, to avoid magnetic sticking: this greatly dampens the impulsive action of the slider on the tool. Moreover, the low working voltage (a 6V or 24V battery) and the presence of a complex mechanism for supplying on/off electric power with a certain frequency cause the device to work with little energy and continuously with a certain frequency, supplying precisely that prolonged and alternate action which has been proved ineffective for the applications considered here.
U.S. Pat. No. 2,480,451 illustrates a device which provides again a low-energy, vibrating/oscillating movement of a tool, under the impulse of an alternated current. Such device is conceived to impart an alternate pressure of varying entity, but the force is minimal and prolonged in time, because it is sufficient, for example, to compact the filling in a tooth.
U.S. Pat. No. 6,171,312 concerns a controlled osteotome. In this case the tool is moved through cam system which are unable to impart any impulsive force, but rather a repetitive and low-modulus force. Through gears and crank gears it is not possible to express effective impulsive forces, because the inertial forces and the numerous couplings prevent from transferring translational momentums in a short time. As a drive system, the use of a cursor movable under the action of a solenoid operating alternately in an excited/disexcited mode is also generically suggested; no specific configuration nor solenoid operation mode is provided; on the basis of how the solenoid is shown, moreover, it does not even seem that it is able to impart a significant action: as a matter of fact, due to the shape of the magnetic field, the cursor is always attracted towards the solenoid centre and cannot protrude therefrom by a length greater than half the length thereof.
All these devices are designed to have a continuous and low-modulus movement, so as to perform mainly an erosive action. This result is the opposite to what has been obtained by the manual technique of the osteotomes beaten by the surgical hammer, which technique can be considered the most valid one to obtain bone mass compacting, but which carries the disadvantages set forth above.
The Applicant has realised that the energy transferred by these devices—through alternate, low-intensity forces, and prolonged over periods of time—is not adequate for obtaining an effective result in this specific sector.
Through in-depth studies and subsequent comparison tests, the Applicant has considered it more effective to fully shift the problem approach, by supplying a tool which, despite using overall power levels equivalent to the known ones (to be able to resort to conventional electric network supplies available in medical surgeries), distributes the energy in a definitely different and original manner, which is more effective for this specific application.